In the last decade, a large number of power generating plants were constructed worldwide, upon which is based a combined gas and steam turbine process, and by which the pollutant emission can be significantly reduced. These power generating plants are designated in technical jargon as combined cycle power generating plants.
In a subform of the combined cycle power generating plant, in the so-called IGCC power generating plants (“IGCC” is an abbreviation for “Integrated Gasification Combined Cycle”), the combined cycle power generating plant additionally has an integrated fuel gasification, by means of which a liquid or solid fuel, for example hard coal, is converted in a gasifier into a synthesis gas, which is then combusted in a gas turbine. As a rule, a purification of the synthesis gas takes place before the combustion. Generally speaking, pollutants are separated before the combustion in this manner, or arise hardly at all in the first place.
Oxygen is required for the gasification of the fuels into synthesis gas. For the producing of the oxygen, IGCC power generating plants have air fractionation plants in which particularly nitrogen is produced from the environmental air by fractional distillation, in addition to the required oxygen. The synthesis gas has to be cooled down before the further treatment. In this connection, a steam develops, which contributes to electric power generation in the steam turbine of the IGCC power generating plant. After the cooling down of the gas, first filters keep back ash particulate, then carbon dioxide can also be extracted, if required. Other pollutants, such as sulfur compounds or heavy metals, are also bound by chemical and physical processes. As a result of this, the required fuel cleanliness for the operation of the gas turbines and for low emissions of the IGCC power generating plant is realized.
The synthesis gas is mixed with nitrogen from the air fractionation plant, and/or with water steam, before the combustion chamber of the gas turbine, in order to suppress the formation of nitrogen oxide. The working gas which then ensues from the combustion with air is expanded in the turbine stages of the gas turbine.
After expansion of the working gas in the gas turbine and subsequent waste heat utilization in a steam generator, the flue gas is discharged to the atmosphere.
The steam flows from the crude gas and flue gas cooling are combined and, together, fed to the steam turbine. After the expansion in the steam turbine, the steam is condensed via a condenser, and the condensate is returned via the feed water tank to the water or steam circuit, as the case may be.
The gas and the steam turbine (a combined cycle power generating plant, or an IGCC power generating plant, as the case may be) are coupled to a generator in which the rotational work of the turbines is converted into electrical energy.
Combined cycle power generating plants, or IGCC power generating plants, as the case may be, are constantly being developed. In this connection, the aim is pursued, inter alia, of constantly increasing the efficiency or the power output of these power generating plants, as the case may be.